Turn signals

The lower brake lites and turn signals use the same bulb filament, just not at the same time. When you turn left, the left turn signal should work, no brake lite on that side. The other brake lites should work. The lower brake lites are wired through the turn signal switch. At the lower rear lites, the dark green wire with brown tracer is voltage for stop or turn. The black wire with yellow tracer is voltage for tail lamps. Black wire is ground. My first thought is a problem with turn signal switch? If you think it is a ground issue, run a redundant ground, see if it helps?